3GPP has defined two technologies to manage CS calls (e.g. voice calls) in EUTRAN: CS over PS (CSoPS) and Voice over IMS (VoIMS over LTE). Each of these two technologies requires a specific handover procedure from EUTRAN to GERAN/UTRAN, i.e., CSoPS handover for CSoPS, or Single-Radio Voice Call Continuity (SRVCC) for handover from VoIMS over LTE to CS GERAN/UTRA.
For both SRVCC and CSoPS technologies, the CS IRAT handover from GERAN/UTRAN to EUTRAN is not defined and is considered as for further study in the standard. It can be assumed that, similarly to any other handover technologies (like CS 2G/3G, PS 2G/3G, LTE, CS GAN (Generic Access Network)), the CS IRAT handover from GERAN/UTRAN to EUTRAN will be using a reverse sequence than the CS IRAT handover from EUTRAN to GERAN/UTRAN. This means that, for both cases, the RNC/BSC initiates the handover by sending a “Handover Required” message to the MSC/VLR to manage the handover.
FIG. 1 illustrates different routing paths for transmitting a handover message from the Radio Access Network of the 2G/3G Network (GERAN/UTRAN: GSM Radio Access Network-UMTS Terrestrial Radio Access Network) to Radio Access Network of the LTE Network (EUTRAN—Evolved Universal Terrestrial Radio Access Network).
It is then expected that for SRVCC, the MSC/VLR triggers the Handover by sending a message to MME (Mobility Management Entity), via the Sv interface (MME-MSC/VLR) which is the reference point defined for handling the SRVCC handover between 3GPP E-UTRAN/UTRAN (HSPA) and 3GPP UTRAN/GERAN, and for CSoPS, the MSC/VLR triggers the Handover by sending a message to IWF, via the A/Iu interface which is known to support the handover in GERAN/UTRAN and which is reused by CSoPS technology.
Consequently, for a network supporting both SRVCC and CSoPS IRAT handover from GERAN/UTRAN to EUTRAN, two different routing paths are possible in MSC/VLR for transferring the Handover Required message. So there is a need to identify to which target node (IWF for CSoPS or MME for SRVCC) the MSC/VLR shall transfer the “Handover Required (target eNodeB cell ID)” message received from RNC/BSC.